Motor vehicle occupant sensing systems

ABSTRACT

A roof-mounted passenger position sensor array of capacitive coupling passenger position sensors, to determine position and motion of a passenger by analysis of distances of the passenger to the various sensors of the array and analysis of the changes of said distances with time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 08/311,576, entitled "Automobile Airbag System", toPhilip W. Kithil, filed on Sep. 23, 1994, now U.S. Pat. No. 5,602,734,and CIP of of U.S. patent application Ser. No. 08/535,576, entitled"Impaired Vehicle Operator System", to Philip W. Kithil, filed on Sep.28, 1995, now U.S. Pat. No. 5,691,693, the teachings of both of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention concerns systems for sensing characteristics ofmotor vehicle occupants for purposes such as deployment of air bagsduring vehicle crashes. More particularly it concerns systems in whichthe system operation is affected not only by information about themotion of the vehicle caused by crash forces, including angularacceleration, but also measured data concerning the motion of thepassenger, so that the system will operate in a manner to minimize therisk of serious injury to the passenger, and will not operate when theair bag deployment would not likely be beneficial.

2. Background Art

Automobile air bag systems are a well known means of attempting toreduce the likelihood of serious injury to passengers in collisions.These systems are designed to very quickly inflate an air bag in frontof a passenger during a collision, so as to hopefully prevent thepassenger from colliding with hard objects in the passenger compartmentinterior, particularly the steering column and/or the dashboard. Suchsystems typically sense that the vehicle is involved in a collision, byusing an accelerometer to sense sudden deceleration of the vehicle.Rapid inflation of the air bag may be obtained by electrical ignition ofa pyrotechnic substance which rapidly generates a volume of gassufficient to inflate the air bag, or by electrical opening of a valvefor release of compressed gas stored in a chamber which is part of theair bag system.

The performance of an air bag system, in terms of its success or failurein preventing serious passenger injury, may be critically dependent onfacts concerning the initial position and subsequent motion of thepassenger, which are not made known to the system by an accelerometerwhich senses deceleration of the vehicle as a whole. Passenger headmotion is particularly important, due to the seriousness of headinjuries. For example, if the passenger is seated too far forward, orhas his/her head too far forward, occupying the space into which the airbag will deploy, the passenger may be seriously injured by thedeployment of the air bag intended to prevent passenger injury. So thereis clearly a need for passenger position sensing apparatus, which canprevent air bag deployment when the passenger is already too far forwardwhen the collision begins.

But even if the passenger is not too far forward at the beginning of thecollision, the passenger will tend to move rapidly forward, with thepassenger's head leading that motion, relative to the vehicle, as thevehicle rapidly decelerates, and will tend to move into the air bagdeployment space, at least in the case of forward collisions, and may betoo far into the air bag deployment space, before the completion of airbag deployment, to escape injury from the air bag deployment. There area number of factors which may strongly influence the forward motion ofthe passenger, in addition to initial position, in ways which may varymarkedly from one passenger to another. The relative forward motion ofthe passenger will depend strongly on whether the passenger has secureda seat lap belt and/or shoulder harness prior to the collision. Thepassenger's motion may also be influenced somewhat by the strength ofany tensing up reaction the passenger has to the collision, i.e.,instinctively pushing forward with the feet against the floorboard torestrain forward motion of the body. Such a protective reaction may varygreatly from one passenger to another, and may be greatly reduced orwholly absent if the collision is too sudden, so that the passenger hasno time to react, or if the passenger is intoxicated or otherwiseimpaired. Also variation of the crash intensity by itself will causeconsiderable variation in passenger acceleration. So there is a need forsystems which measure the position vs. time of the passenger,particularly head motion, and analyze that information in making the yesor no decision on air bag deployment. Although systems are known whichmeasure passenger motion, as described in documents filed withapplicant's Information Disclosure Statement, applicant is not aware ofsuch a system employing an overhead array of capacitive couplingproximity sensors, as in the present invention, to continuouslydetermine passenger position by triangulation, and determine passengeracceleration by means of a microprocessor which analyzes signalsindicative of passenger distance from each sensor of the array, andchanges of said distances with time. Overhead sensors offer an advantageover those previously known systems having beam-emitting sensors locatedin front of the passenger, as in air bag systems with acoustic sensorsmounted on the steering column, for which the beam from the sensor willat times by blocked from operating by the hands and/or forearms of thedriver.

The use of an array of capacitive coupling proximity sensors offersadvantages over beam-emitting sensors, in an air bag system, since eachcapacitive coupling sensor functions by sensing the change in thecapacitance of a capacitor, caused by the nearby presence of a person,an effect which is essentially instantaneous (since propagated at lightspeed), rather than requiring a finite, non-negligible beam travel timeas in the case of an ultrasonic position sensor, and since thecapacitive coupling sensor does not require transmission and detectionof a beam which might be blocked. And the use of the overhead array ofcapacitive coupling proximity sensors, the signals from which areanalyzed by the microprocessor, allows essentially instantaneous andcontinuous monitoring of passenger position and motion throughtriangulation based on the distances of the passenger to the varioussensors of the array, so that the overhead sensor array can be used toaccurately and continuously determine fore-aft, diagonal, and lateralpassenger motion. Since the passenger's head will be closest to theoverhead sensors, this method will be particularly sensitive topassenger head motion.

The present invention also addresses a need for an air bag systemsensitive to angular vehicle acceleration, for both crash confirmationpurposes and also to prevent air bag deployment in the case of a vehiclerollover, in which case air bag performance may be unreliable anddeployment is undesirable. This need is met through use of a three axisvehicle rollover sensor, the output of which is analyzed by themicroprocessor.

The present invention also addresses a need for an air bag system thatwill provide protection against injury of a forwardly positionedpassenger, which might otherwise be caused by the air bag deployment, inparticular an infant sitting in a conventional rear-facing infant carseat, conventionally positioned with the child's head rather farforward, where the child may suffer a serious head injury during air bagdeployment. As detailed below, this need is met by the provision of anair bag which, when inflated and deployed, has two principal chamberswith a reentrant slot between them, which slot can accommodate theinfant in the car seat, and which geometry allows deflection of therearmost of the two chambers by the car seat and infant, to reduce theforce of impact with the passenger and thus reduce the risk of such aninjury.

Since the design of automotive air bag systems continues to evolve, asmore knowledge is gained about the dynamics of crashes, includingproblems associated with variations in passenger motion during a crash,there is a need, for crash investigation purposes, for a system whichcan record the vehicle and passenger motion during the crash process,particularly passenger head motion. This need is met by the presentinvention, through the provision of recording means in themicroprocessor connected to the sensors which detect vehicle andpassenger motion.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

The present invention is of a roof--mounted motor vehicle air bagsystem, having, as principal components: a roof-mounted array ofcapacitive coupling passenger position sensors, for continuously sensingpassenger position, especially head motion, by means of triangulationanalysis of distances from the passenger to various sensors of thearray; a rollover sensor for continuously monitoring all three vehicleaxis orientations; a microprocessor, for analysis and brief recording ofoutputs of the passenger position and rollover sensors, and generationof a signal for air bag deployment, also having in its memory severaldata bases which are tables of values representative crash-relatedparameters, further described below; a pyrotechnic gas generator meansfor air bag inflation, upon receipt of the firing signal from saidmicroprocessor; and a multi-chamber air bag, intended for passenger use(though the other components of the present invention could also be usedwith driver, side, or rear seat air bag systems), having two principalchambers, separated by a reentrant reaction surface, with one chamberpositioned for deployment, on inflation, along the inner surface of thevehicle windshield, and the other principal chamber deploying to therear of the first, and with the rear most of the two chambers beingdeflectable by a forwardly positioned occupant such as an infant in arear-facing child car seat of the kind customarily placed in a forwardposition, which car seat would lie within the slot formed by reentrantreaction surface, to reduce the risk of passenger injury from air bagdeployment. The passenger position sensors are proximity sensors, whichare capacitors with associated circuitry to continuously monitor theeffect on the capacitance value caused by the presence of a person inthe vicinity, which effect is dependent on the distance from the personto the sensor. By use of an oscillator and signal processing circuitrythe preferred embodiment monitors the changes in the capacitive couplingeffect with suitable sampling frequency, so that the array can be usedto measure movement of a passenger. The microprocessor is programmed todeploy the air bag if the sensor data, as compared with a crashconfirmation data base table, indicates a crash (this data base tablecontains data, for comparison purposes, on normal motion which would notbe indicative of a crash, e.g. head motion from a sneeze); however themicroprocessor is programmed to not issue a firing signal if either:comparison of occupant position and velocity data from the passengerposition sensor array, with "no fire" data base figures in tablesshowing air bag position during deployment, indicates that the occupantwould interfere with the deploying air bag; or if a likely vehiclerollover is indicated by the microprocessor's comparison of data fromthe rollover sensor with tables of values indicating a vehicle rollover,or if data from the rollover sensor indicates that angular vehicleacceleration is insufficient to indicate a collision; or the sensor dataindicates that the passenger's motion would not be restrained by the airbag, because of the direction of motion of the passenger caused by thecrash, e.g. in a crash with substantial lateral crash force components,causing substantial lateral passenger motion.

The invention is of a method of and apparatus for disabling an airbagsystem for a seating position within a motor vehicle, the airbag systemcomprising an airbag door, comprising: providing to a roof above theseating position one or more capacitive coupling occupant sensors;detecting presence or absence of an occupant of the seating positionusing the one or more capacitive coupling occupant sensors; disablingthe airbag system if the seating position is unoccupied; detectingproximity of an occupant to the airbag door if the seating position isoccupied; and disabling the airbag system if the occupant is closer tothe airbag door than a predetermined distance. In the preferredembodiment, modifying airbag deployment parameters to adjust inflationforce of the airbag according to proximity of the occupant to the airbagdoor is included. Two capacitive coupling sensors may be used, anddetecting proximity is done by providing voltage output values of thecapacitive coupling sensors to a data processor and comparing thevoltage output values against predetermined values to determine occupantposition. Preferably, one capacitive coupling sensor is forward of themidpoint of the seating position and one aft of the midpoint.

The invention is also of a motor vehicle air bag system for inflationand deployment of an air bag in front of a passenger in a motor vehicleduring a collision, the motor vehicle having a passenger compartment forat least one passenger in the motor vehicle, the passenger compartmenthaving an interior roof and a passenger seat for the passenger, the airbag system comprising: an air bag; inflation means connected to the airbag for inflating the air bag with a gas; passenger sensor means,mounted adjacent to the interior roof, for continuously sensing positionof the passenger with respect to the passenger compartment, and forgenerating electrical output indicative of the position of thepassenger; analog processor means, electrically connected to thepassenger sensor means and to the inflation means, for comparing andperforming an analysis of the electrical output from the passengersensor means, and for activating the inflation means to inflate anddeploy the air bag when the analysis indicates that the vehicle isinvolved in a collision and that deployment of the air bag would likelyreduce a risk of serious injury to the passenger which would existabsent deployment of the air bag and likely would not present anincreased risk of injury to the passenger resulting from deployment ofthe air bag.

The invention is further of a capacitive coupling sensor arraycomprising a first sensor having a first geometry and a second sensorhaving a second geometry, the first and second sensors being placed suchthat equipotential lines of the first and second sensors overlap. In thepreferred embodiment, the first and second geometries are circular,oval, square, rectangular, triangular, or polygonal of greater than foursides. The sensor array is preferably mounted proximate a roof of amotor vehicle, a long axis of the first sensor is perpendicular to along axis of the second sensor, the first geometry is rectangular andthe second geometry is oval, and the first sensor is rearward of thesecond sensor in the motor vehicle.

The invention is additionally of a vehicle occupant sensing systemcomprising one or more capacitive coupling sensors, the sensorscomprising a receive electrode and a drive electrode, the receiveelectrode placed within the drive electrode such that a spacing betweenedges of the receive electrode from the drive electrode isnon-homogenous, the sensors generating equipotential field lines ofnon-uniform curvature. In the preferred embodiment, the sensors aremounted proximate a roof of a motor vehicle.

The invention is also of a vehicle occupant sensing system comprisingone or more capacitive coupling sensors, the sensors comprising aflexible circuit board adhered and electrically contacted to a flexibleconnector. Preferably, the sensors are mounted on a curvilinear portionof a roof of a motor vehicle.

The invention is further of a dynamically variable capacitive couplingsensor comprising at least three electrodes in a concentric arrangement,each of the electrodes being sequentially configurable as a driveelectrode, grounded gap, and receive electrode. Preferably, the sensoris mounted proximate a roof of a motor vehicle and is comprised by anoccupant sensing system of the motor vehicle.

The invention is also of, in a roof-mounted, occupant capacitivecoupling sensor system, a method of and apparatus for determiningcharacteristics of an occupant's head, comprising: providing more thanthree fringe field capacitive coupling sensors to a roof of a motorvehicle; for each sensor, determining proximity of the head by means ofthe sensor's fringe field; and determining from the proximities to eachsensor an approximate center and orientation of the head. In thepreferred embodiment, an approximate diameter of the head is determinedby initially assuming an approximate diameter and then iterativelyrefining the approximate diameter by determinations of position of thehead employing a subset of the sensors. Approximating body mass fromhead position and dimensions may be performed if desired.

The invention is also of a roof-mounted capacitive coupling occupantsensing system comprising circuitry for determining an average ratherthan an instantaneous position of an occupant of a motor vehicle.Preferably, the circuitry comprises a time delay circuit (e.g., anastable multivibrator), and the time delay circuit comprises a devicefor disabling reporting of a condition unless the condition has existedfor a predetermined period of time.

The invention is further of an apparatus for determining and analyzingcharacteristics of a motor vehicle seating position occupiable by anoccupant, the apparatus comprising a roof-mounted capacitive couplingsensor array and circuitry for performing a function by means of thearray. The functions covered by the invention include: providing arecord of head acceleration of the occupant; notifying authorities of atotal number of occupants in the motor vehicle; controlling heating andcooling systems of the motor vehicle; controlling sound systems of themotor vehicle; recording seat occupancy over time; automaticallyadjusting side-mirrors; automatically adjusting seat position;automatically adjusting a seat headrest; providing an alarm if anoccupant occupies the seat position for more than a predetermined periodof time without a key being in an ignition device of the motor vehicle;and automatically adjusting position of a sighting device.

Other objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate several embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating a preferred embodiment of the invention and are not to beconstrued as limiting the invention. In the drawings:

FIG. 1 is a side elevational view of the system of the presentinvention, partially in section;

FIG. 2 is a plan view, showing the array of capacitive couplingproximity sensors;

FIG. 3 is an expanded view of the portion of FIG. 1 showing the foldedair bag, prior to deployment;

FIG. 4 is a side elevational view showing the air bag in a partiallyinflated configuration;

FIG. 5 is a side elevational view showing the air bag in a fullyinflated configuration, and also showing a rear-facing infant car seat;

FIG. 6 is a side elevational view showing the air bag in a fullyinflated configuration, and also showing an adult passenger;

FIG. 7 shows the detector element and also schematically shows thesignal processing circuit, which together form one of the proximitysensors of the preferred embodiment;

FIG. 8 shows a side elevational view of one of the proximity sensors,above the head of a passenger;

FIG. 9 is a plan view of an arrangement of a "breadloaf" and an ovalsensor with overlapping field;

FIG. 10 is a side view of the arrangement of FIG. 9;

FIG. 11 is a plan view of a non-homogenous capacitive coupling sensorelectrode configuration;

FIG. 12 is a side view of the configuration of FIG. 11;

FIG. 13 is a perspective view of a flexible circuit board sensor withintegrated flex cable;

FIG. 14 is a side view of the configuration of FIG. 13;

FIG. 15 illustrates head orientation and sizing using a three-sensordetector array;

FIG. 16 illustrates head orientation and sizing using three-sensor andfive-sensor detector arrays;

FIG. 17 is a side view of the arrays of FIG. 16;

FIG. 18 is an illustration of use of a three-detector array to detecthead orientation and size;

FIG. 19 is an illustration of use of a five-detector array to detecthead orientation and size;

FIG. 20 is a plot of sensor response for various electrode spacingsuseful in assisting configuration of a non-homogenous capacitivecoupling sensor electrode such as that of FIGS. 11 and 12;

FIG. 21 is a plan view of a variable-geometry circular sensor of theinvention;

FIG. 22 is a side view of possible zones and voltages created by foreand aft sensors having overlapping field further described by Table I;and

FIG. 23 is an illustrative decision tree to determine total body massfrom detected head size.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUTTHE INVENTION)

Referring now to the drawings, in which like reference numbers denotelike or corresponding elements, the principal components of theroof-mounted air bag system of the present invention, are a positionsensor array 10 of capacitive coupling proximity sensors 12, a rolloversensor 14, a microprocessor 16 (which may be analog or digital or ahybrid thereof), a gas generator means 18, and an air bag 20, eachfurther discussed below.

The components of the system are attached to a mounting plate 22 abovethe headliner 24 which is held in place against the passenger cabin roofby edge molding, adhesives, and/or fasteners. The mounting plate 22 issecured by bolts or other secure attachment means at its front end, tothe windshield header 26, a part of the vehicle used to attach thewindshield 28 to the forward edge of the vehicle roof 30. The mountingplate 22 is firmly secured at its rear end, e.g., by bolts or welding,to a cross brace 32, a standard brace which extends transversely acrossthe interior of vehicle roof 30.

The gas generator means 18 is housed within a manifold 34, whichmanifold is firmly secured, e.g., by bolts or welding, to mounting plate22. The gas generator means 18 conveys gas to air bag 20 through a gasnozzle 36. As shown in FIG. 3, air bag 20 is compactly folded aboveheadliner 24, when not inflated and deployed. The headliner 24 has athin breakaway or door portion 38 below air bag 20, to allow deploymentof air bag 20 during a collision.

The proximity sensors 12 forming the position sensor array 10 may beattached to mounting plate 22, or embedded in headliner 24.

The rollover sensor 14, adjacent to position sensor array 10, issecurely attached, e.g., by screws, to mounting plate 22. Themicroprocessor 16 is also securely attached to mounting plate 22.Electric power for operation of microprocessor 16, may be obtained byrunning wires 40 down one of the A-pillars 42, as shown, oralternatively by running the wires 40 to the dome lamp (not shown). Abackup power supply may be a battery 44 and/or a capacitor 46, alsoattached to mounting plate 22. The air bag system is covered byheadliner 24, which is an insulating and cosmetic material such asfoamboard, urethane composites, etc., which is securely attached byadhesive or by edge molding structures or other secure means to theinner surface of vehicle roof 30, and to mounting plate 22.

Each of the proximity sensors 12 consists of both a detector element 48,and a signal processing circuit 50, which are best illustrated in FIG.7. The detector element 48 consists of at least two conductors on oneside of a printed circuit board 52, shown in the particular embodimentof FIG. 7 as an oscillator input loop 54, and detector output loop 56.The proximity sensors 12 each function by creating an electrostaticfield between oscillator input loop 54 and detector output loop 56,which is affected by presence of a person near by, as a result ofcapacitive coupling, due to the fact that the human body hasconductivity and a dielectric constant different from those of air. Thusthere is a change in the capacitance between oscillator input loop 54and detector output loop 56, caused by the presence of a person nearby.As is well known in the electronic arts, such a capacitive couplingeffect will be dependent on the distance from the person to sensor 12.The measured capacitance change may thus be used to determine thedistance of the person from sensor 12. The purpose of the signalprocessing circuit 50, with oscillator 58 and charge-sensitive amplifier60, is simply to continuously monitor the capacitive coupling effect,and changes in the magnitude of the effect, so that the microprocessor16 will continuously receive signals from each of the proximity sensors12, indicative of passenger position. The signals will be particularlysensitive to passenger head position and head motion, since the head isclosest to the overhead position sensor array 10. The oscillator 58 isoperated at a frequency of the order of 100 kHz, and signal processingcircuit 50 will sample at 10 kHz, which is adequate for continuous rapidsampling of the capacitive coupling effect, and changes therein.

The sampling rate for signal processing circuit 50 may be determined bymeans contained within microprocessor 16, such as a conventionalanalog-to-digital converter circuit if the microprocessor operatesdigitally. The signal processing circuit 50 may consist of aconventional full wave rectifier and a conventional peak detector,connected in series. The position sensor array 10 is an array of theproximity sensors 12 having both longitudinal and lateral extension, asbest shown in FIG. 2. An array of one detector every 6" to 121" isbelieved to be suitable, i.e., the array above a passenger consisting of4 to 8 detectors depending on the vehicle. An array for bench seats mayrequire more detectors than an array for bucket seats, due to greatervariation in occupant position in the seat. The array is used forpassenger position determination, as explained below.

The rollover sensor 14 is an electronic 3--axis compass, having threeelectrical outputs indicative of rotation of rollover sensor 14 abouteach of its axes. The output signals from rollover sensor 14 are sent toinputs of microprocessor 16 by wires (not shown), so that microprocessor16 may continuously analyze data regarding components of angular vehicleacceleration.

The microprocessor 16 is programmed to perform the following functions.At startup of the vehicle ignition, which turns on power tomicroprocessor 16, the microprocessor 16 turns on power to each of theproximity sensors 12 of position sensor array 10, and to rollover sensor14. The microprocessor 16 continuously monitors the distance of theeffective electronic center of a passenger from each of proximitysensors 12, by comparing the capacitive coupling effect produced in eachof proximity sensors 12, with a lookup table containing capacitivecoupling effect correlations to distance, stored in the memory of themicroprocessor 16. By triangulation from the distances of the passengerto the three closest proximity sensors 12 of position sensor array 10,the microprocessor 16 continuously computes and updates the passengerposition, as the output signals from each of proximity sensors 12,continuously driven by oscillator 58, are continuously received andanalyzed by microprocessor 16. The memory of microprocessor 16 is of asize sufficient to contain the most recent 50,000 passenger positions,corresponding to about five seconds of sensing (at the 10 kHz. samplingfrequency of oscillator 58), after which newer data overwritespreviously recorded data. Thus the microprocessor 16 will contain adetailed record of passenger position during the last five secondsbefore a crash, and will continue to record data for five seconds afterthe crash, which will be quite useful for later crash analysis purposes.Air bag deployment will stop the erasure of old data.

The microprocessor 16 memory also contains passenger head motion lookuptables of threshold acceleration values which may be used to distinguishlesser acceleration motions which often occur in non-collisionconditions, e.g., head motion from a sneeze.

The microprocessor 16 is programmed to make a preliminary decision fordeployment of air bag 20, if 30-50 or more successive passenger positiondata points in the memory show an increasing passenger acceleration, andif comparison of this passenger motion data with the parameters in thepassenger motion crash parameter lookup tables, indicates a collision.However, the microprocessor 16 is also programmed to override thepreliminary decision for air bag deployment, under several different andalternative circumstances:

The microprocessor 16 also simultaneously computes the projectedpassenger motion during air bag deployment, using the same 30-50 mostrecent passenger position data points, and thus determines the likelyaverage position of the passenger during the early expansion phase ofair bag deployment. The microprocessor 16 compares this position to a"no fire" lookup table contained in the memory of the microprocessor,containing representative positions (three dimensional coordinates)which would be occupied by air bag 20 after initiation of deployment,during its early expansion phase, i.e., from the initial stored positionuntil air bag 20 has extended down to the top of the dashboard(passenger air bag) or to the midpoint of the steering wheel (driver airbag). The microprocessor 16 is programmed to override the preliminarydecision for air bag deployment, if the projected average passengerposition during air bag deployment is within the "no fire" zone, or tooclose--within some chosen safety margin distance.

The microprocessor 16 also continuously samples the signals from therollover sensor 14, reflecting rotation of the x, y, or z vehicle axes.The rollover sensor 14 transmits this data to microprocessor 16 at arate of 5 kHz. and this data is sampled and recorded at a rate of about20%, or 1 data point per millisecond. The microprocessor 16 isprogrammed to override an initial decision for air bag deployment, basedon analysis of the signals from rollover sensor 14, in two situations.First, the angular acceleration data for the sampled data points, iscompared with data stored in the memory of microprocessor 16 in a"rollover therefore cancel" lookup table, which table has values ofaxial accelerations indicative of a vehicle rollover. If this comparisonindicates that the vehicle will likely roll over from the presentcollision, air bag deployment is canceled, because air bag performanceis unpredictable and possibly harmful in a vehicle rollover; forinstance, the occupant could be propelled into the roof rather thanforward into the steering wheel or dashboard. Second, the same datapoints of angular acceleration are compared with a "crash confirmation"table stored in the memory of microprocessor 16, having minimum valuesof angular accelerations which are indicative of true collisions. If theangular acceleration for the three axes is less than these lookup tablevalues, air bag deployment is cancelled. In other words, at least one ofthe measured angular accelerations must exceed the corresponding minimumvalue in order for deployment to occur.

If the preliminary decision for air bag deployment is not overridden bythe microprocessor 16, in one of the ways explained above, themicroprocessor 16 initiates deployment of air bag 20, by sending anelectrical signal to the gas generator means 18.

In certain vehicles, it may be preferable to employ analog circuitry togeometrically determine head position, allowing virtually instantaneousderivations of head velocity and acceleration. Because digitalmicroprocessors are relatively slow for complex trigonometric functions,a data throughput of approximately one millisecond may be insufficientfor airbag triggering in high speed crashes. By using analog computingcircuitry, the data throughput is much greater, providing thousands ofdata points per millisecond. This data rate is comparable to theoperating rates of micromachined accelerometers, yet relies on actualmeasurements of the occupant rather than a remote sensing device toactivate the airbag. This can improve reliability and airbag deploymenttiming. As an example, signal processor 50 can output voltage signalsfrom each sensor to analog circuit 16 which transforms each voltage to adistance, which is further processed in analog form to geometricallydetermine head position. This is expressed as three voltagesrepresenting a position in space. This head position can be time-steppedto derive head velocity and acceleration. Use of analog circuitry makesanalog/digital conversion unnecessary, and eliminates the need for adigital microprocessor to perform the geometric algorithm and re-convertthe results back to analog form of x,y,z coordinates. The onlyrequirement for digital conversion may be for brief storage of data,which can be accomplished with custom digital circuit and FIFO storagedevices.

The gas generator means 18 is a means to rapidly generate a large volumeof gas for inflation of air bag 20, in response to an electrical signalfrom microprocessor 16. Preferably this is accomplished through ignitionby squibs (not shown), triggered by the firing signal frommicroprocessor 16, of a pyrotechnic gas generation mixture containedwithin two gas generator chambers connected to air bag 20 by a singlegas nozzle 36. The inflation of air bags by gas generated throughburning of pyrotechnic mixtures, which may be ignited electrically byone or more squibs, is an air bag inflation method well known in theart, as described for example in the patent on the invention of Cuevas,U.S. Pat. No. 5,058,921, describing combustion chambers 32 and 34containing a mixture of sodium azide and copper oxide, ignited by asquib 36. Col. 6, lines 56-68; FIG. 2; Col. 7, lines 37-41; and thepatent on the invention of White et al, U.S. Pat. No. 5,071,160,describing air bag inflation by a plurality of pyrotechnic-activated gasgenerating cartridges 44. Col. 5, lines 22-37. Said disclosures of saidpatents are incorporated herein by this reference.

The air bag 20 of the present invention is a multi-chamber air baghaving a deployed configuration which is intended to reduce the risk ofserious injury to a forwardly positioned passenger, specificallyincluding an infant who may be forwardly positioned in a conventionalrear-facing child car seat. The design also provides enhanced cushioningeffects to reduce the risk of occupant injury.

The air bag 20 has a first chamber 62, forming a neck which extendsaround gas nozzle 36, to which first chamber 62 is securely attached bya suitable clamp 64, or other suitable attachment means. The air bag 20is configured to form, on inflation, two principal chambers, a forwardchamber 66, which inflates downward with its forward surface 68extending downward along windshield 28, and a rear chamber 70. Areentrant notch 72, of the form of an inverted V, is formed by areentrant reaction surface 74, the portion of the surface of air bag 20joining forward chamber 66 and rear chamber 70. The reentrant notch 72is maintained, against the tendency of the gas pressure to erase it byforcing downward the juncture between forward chamber 66 and rearchamber 70, by means of an tether 76 within air bag 20, which attachesthe top of air bag 20 to the juncture between forward chamber 66 andrear chamber 70.

This geometry tends to reduce the risk of injury to an infant in arear-facing car seat, or other forwardly positioned passenger, sincethis passenger can fit within notch 72 between forward chamber 66 andrear chamber 70, and since the body of a forwardly positioned passenger,even if sufficiently far back as to be struck by rear chamber 70, candeflect rear chamber 70 upward, so as to reduce the impact on thepassenger from the collision with the air bag 20.

The air bag design also provides an enhanced cushioning effect, sincethere is a sequential flow of the gas from first chamber 62, to forwardchamber 66 and thence to rear chamber 70. Gas may be vented through oneor more orifices (not shown) in air bag 20, or if a porous fabric isused in fabrication of air bag 20, some of the gas may seep out of thepores, thereby providing a soft cushioning effect.

Those familiar with the art will appreciate that the invention may beemployed in configurations other than the specific forms disclosedherein, without departing from the essential substance thereof.

For example, and not by way of limitation, other forms of capacitivecoupling proximity sensors could be used, other than the specific formdisclosed herein, provided only that the sensor element has acapacitance between two of its electrodes, and that the sensor circuitis able to measure changes in said capacitance caused by capacitivecoupling effects of the head of the passenger. Or the means forcalculating passenger position and acceleration could use the elementsdisclosed in applicant's prior patent application no. 08/130,089, filedSep. 30, 1993, entitled "AUTOMOBILE AIR BAG SYSTEM", e.g., at page 11,line 25-page 12, line 10.

It would of course not be necessary to use a squib-fired pyrotechnicmixture for the gas generation means; one could instead employ apressurized gas container, with an electrically operated valve activatedby a firing signal from the microprocessor.

Similarly the invention is not to be regarded as being limited to anyparticular choices of the spacing dimensions of the proximity sensors 12in position sensor array 10; or of the sensor operating rates orsampling rates; or of mounting methods inside headliner 24, orparticular methods of attachment to the roof structure; or to the use ofa particular vehicle linear accelerometer as part of the crashconfirmation process, such as Analog Devices ADXL50, rather than thethree-axis angular accelerometer.

Further desirable construction and orientations of the capacitivesensors are next described. The precise construction and orientation maybe varied to achieve desired results for particular vehicles.

One manner in which to determine occupant position is to use two sensorsproviding voltage output to the microprocessor, representing thecapacitive coupling effect of the occupant's position relative to eachsensor. The microprocessor can compare these voltages against knownvalues indicating occupant zone position, without referring to avoltage-distance translation function. This configuration isparticularly useful for vehicles having inadequate roof space for anarray of three or more sensors. Also, because sensor response diminishesexponentially with distance, triangulation methods to determine theposition of a small person whose head is located farther from theroof-mounted sensor array may yield incorrect data. Because the logicand software algorithm to generate zone position needed by a dual sensorarray is simpler than a triangulation algorithm, the dual sensor arraycan provide more reliable zone positioning at far range, compared to thetriangulation algorithm. The latter, which requires data from threesensors, outputs an error condition if the occupant moves out of rangeof one of the sensors.

Referring to FIG. 22, the two sensors 12 are mounted in the headlinerabove each seat, positioned parallel to the longitudinal axis of thevehicle, i.e., one forward and one aft of the seat midpoint. Because thesensing fields overlap, extending downward approximately 20" from eachsensor, multiple zones are created, consisting of voltage responses to ahuman occupant from each of the two sensors. A table of possible zonescreated by various sensor responses are shown and depicted below:

                  TABLE I                                                         ______________________________________                                        Aft Sensor          Fore Sensor                                                                              Airbag System                                  Zone   ID       Volts  ID     Volts                                                                              Inflator Level                             ______________________________________                                        A      far      3 to 4 far    3 to 4                                                                             3                                          B      close    <3     close  <3   3                                          C      close    <3     far    3 to 4                                                                             4                                          D      far      3 to 4 close  <3   2                                          E      out      >4     close  <3   1                                          F      out      >4     far    3 to 4                                                                             off                                        G      close    <3     out    3 to 4                                                                             5                                          H      far      3 to 4 out    >4   5                                          ______________________________________                                    

The zones, voltages, and airbag system response can be varied to suitthe requirements of the vehicle dimensions and airbag system parameters.

The zoning concepts achieved with two sensors are feasible for a varietyof sensor geometries, including round, rectangular, and polygon-shapedsensors. By use of non-round sensors, the sensing fields can be tailoredin shape to match the dimensions of most positions of a seated occupant,including upright or fully reclined seatback, seat positioned fullforward or aft, and occupant resting against the door or window. Theapproximate sensing fields for two exemplary detector shapes 12 aredepicted in FIGS. 9 and 10.

Because the equipotential field lines for a round sensor arehemispheric, the use of this shape in the front seat of a vehicle mayresult in the field lines infringing on the side window and frontwindshield, or extending behind the front seat. Because the sensor isresponsive to water and "sees through" glass, a heavy rain storm couldpossibly cause a false signal. Or, if the field lines extend behind thefront seat, a rear-seated occupant could cause an unwanted sensorresponse. Therefore, it is desirable to shape the equipotential fieldlines so they more nearly match the preferred interior dimensions of thefront passenger area, with minimal infringement on glass areas or intothe rear seat. This can be accomplished by using a rectangular or"breadloaf" shaped sensor in combination with an oval or round sensor,installing each in such a manner that the equipotential lines areconstrained to the likely positions of a front seat passenger's head, asshown in FIGS. 9 and 10. Such an arrangement provides a field shapeconsistent with fore-aft seat travel and seatback recline, whileminimizing the likelihood of false response caused by water on thewindshield or side window. Preferably, the two shapes are juxtaposed sothat long axis of one is 90 degrees offset from the long axis of theother.

As may readily be understood, various combinations of round, square,breadloaf, oval, and polygon-shaped detectors can be utilized dependingon the sensing volume requirements. Also, the juxtapositioning of twosensors can be arranged in various manners to achieve the desiredresult.

Optimum occupant sensing by roof-mounted capacitive coupling sensorsrequires matching the sensing field volumes to the interior volume ofthe passenger compartment. A means to improve the coincidence of thesevolumes is to vary the spacing between the drive and receivingelectrodes of the capacitive coupling sensors, resulting in a skewing ofequal potential sensing field lines. The sensing field thus can beconfigured to better fit the passenger compartment and to detect anoccupant in all possible seating positions.

An occupant sensing system must be responsive to the passenger occupyinga wide variety of seating positions resulting from the many seatadjustments possible. This responsiveness can be enhanced by utilizingnon-homogeneous spacing of sensor electrodes, which create equalpotential field lines that are skewed to match the desired volume of thepassenger compartment. An exemplary non-homogeneous electrode spacing102 for a round sensor 12 comprising drive electrode 104 and receiveelectrode 106 is depicted in FIGS. 11 and 12, generating equal potentialfield lines 108. Sensor response for various electrode spacings areknown, as shown in FIG. 20, which can assist in determining propernon-homogenous electrode configuration for a given vehicle and desiredresult.

Sensor designs incorporating flexible circuit boards and integrated flexcables may be used to improve the fit of a fringe field capacitivesensor onto the curved portion of a roof headliner, to improve thereliability of the sensor by integrating the connecting cable into thetop layer of the multi-layer circuit board, and to properly connectgrounded layers of the multi-layer circuit board, enabling properfunctioning of the capacitive sensor. A rigid sensor circuit boardinstalled on a curved roof surface requires special adhering techniqueswhich are not optimum considering the life expectancy of vehicles, thepossible heat buildup in the roof, and modern high speed assemblyrequirements. Therefore, it is advantageous to produce the sensor usingflexible circuit board materials, thus allowing the sensor to follow thecurvilinear shape of the roof, at least in the major dimension of roofcurvature.

Furthermore, connectors which physically connect cables or wires tocircuit boards are often subject to stress and vibration, which maycause the connection to come loose. Therefore, it is desirable tointegrate the cable by using a continuous layer of flex circuit boardmaterial as the cable, extending this flex layer as the top layer of themulti-layer circuit board. This layer can be produced as a "daughter"board, meaning it is populated with various active components,integrated circuits, etc., which are integrated electronically with theunderlying layers of the flex sensor circuit board. This design improvesreliability and reduces cost.

Flex circuit boards are typically produced in single and double-sidedconfigurations. Electrically connecting two double sided flex boards isdifficult because the flexibility causes intermittent disconnect of theconnecting circuit pads. Or, if the pads are slightly separated, acapacitor is created, with unpredictable results on the signals. In thepresent sensor design, it is necessary to connect the top and bottomlayers while avoiding any connection between the middle layers.

The preferred flex sensor design 110, showing the integrated flex cable112 incorporating active components 114, is shown in FIGS. 13 and 14.The technique for connecting two double-sided flex circuit boards isshown in FIG. 14. In this illustration, sides 1 and 2 are interconnectedusing conventional surface mount design, as are sides 3 and 4. Toconnect side 1 to side 4, matching holes are drilled through bothlayers, but these holes are insulated from the circuitry on layer 2 byproviding the holes with insulative "doughnuts" (not shown). Then, afterthe two layers are adhered by adhesive and dielectric layer 118, rivets116 are inserted through the holes, and the rivets 116 are mushroomed,thus permanently connecting the flexible cable 112 and the flexiblecircuit board 110. This simultaneously electrically connects side 1 andsides 3 and 4, accomplishing the necessary connections. The rivets canbe accomplished with any conducting material, using a variety ofconnecting devices such as solder, threaded attachments, and the like.The flex sensor and integrated cable can be in a geometry other thanrectangular or circular, and the sensor can incorporate non-homogeneouselectrodes and electrode spacing.

It is known that increasing electrode spacing affects sensor response. Asmaller electrode spacing results in a sharper transition in thevoltage/distance function. Therefore, sensors with multiple concentricelectrodes that sequentially can be electronically connected to thedrive electrode, disconnected and grounded, or connected to thereceiving electrode, can generate a range of voltage responses for anygiven detector and target object. The additional data generated bydynamically varying the sensor geometry can improve discrimination ofthe target. In the case of the human head as target, multiple sensorsusing this process can help determine head orientation, size, and shape,all of which can be used to tailor the output of "smart" airbag systems.The resulting varying sensor outputs can be processed to determineadditional information about objects, including humans, in the field ofview. For example, it is possible to distinguish occupant head size andorientation by reference to the different responses obtained bydynamically adjusting the electrode configuration. This information canthen be used to further refine airbag system deployment characteristics.

A variable-geometry circular sensor is shown in FIG. 21. In this design,the nine rings can be sequentially configured as drive electrode,grounded gap, or inner receive electrode, to arrive at 727 differentpossible configurations of drive electrode, gap, and receive electrode.The principles involved in a round variable-geometry sensor can apply tomost sensor geometries, whether circular, "breadloaf", square, orpolygon in shape. Electrodes can be homogeneous or non-homogeneous.

Fringe field capacitance sensors can determine proximity to the head byreference to transfer functions relating voltage to proximity for thespecified object, in this case a spherical water-filled object of about7" diameter. Determination of proximity from three or more sensorsallows computation of x,y,z coordinates using trigonometric functions.Referring to FIG. 15, because fringing fields 120 generated by sensorsof detector array 10 are surface phenomena, the method initially uses anestimated head diameter of 3.5" to derive the "electronic center" of thehead 122. In side view, this is depicted in FIG. 15. Triangulationrequires the head to be within the range of the most distant detector.By introducing more detectors, a larger array expands the triangulationvolume, depicted in FIG. 16 as an oval 129 encompassing the points ofall possible triangles of the five detectors b1 through b5. FIG. 17depicts in side view the effective volume 134 for determining head x,y,zcoordinates generated by the three-sensor and five-sensor arrays 130 and132 of FIG. 16. In that an oval shaped head is being sensed usingoverlapping hemispheric fields, determination of head orientation ispossible. Additional capabilities include determination of approximatehead diameter and major/minor axes, using arrays with more than threesensors. Depicted in FIG. 18 are overlapping hemispheric fringing fields136 intersected by the oval head 122. As the head changes orientation,x-y coordinate values are affected. To simplify matters, athree-detector array 130 is shown in FIG. 18, but more sensors wouldpreferably be used. Iteration of position from four or more detectorscan derive a good estimate of head diameter. This capability is depictedwith a five sensor array 132 in FIG. 19 (double arrow is for the seconditeration). A system according to present invention can further providea reasonable approximation of body mass by reference to x,y,zcoordinates of the head and head major and minor dimensions. Anexemplary decision tree for estimating mass is provided by FIG. 23.

Capacitive sensing systems operate electronically, and thus are able todetect many occupant positions in a short period of time. Thiscapability is far in excess of the desired response time, and in factcan cause improper toggling of the safety system by triggering thesystem on or off more frequently than desired. A time delay circuit isprovided to slow down the response of the sensor system, reducing thelikelihood of unwanted on/off conditions. Accordingly, it is desirableto modify the response of a roof-mounted capacitive coupling occupantsensor so the sensor responds to the average position of the occupantrather than the instantaneous position.

The electronics circuitry of the present invention preferably includes atimer device (in the preferred embodiment, an astable multivibrator)which activates the toggle condition only if the condition still existsafter the predetermined time delay has expired. If the toggle conditionno longer exists, the system remains in its original state. Any timerwhich is small, lightweight, accurate, and preferably inexpensive can beused for this function.

While the present invention is primarily useful for sensing a vehicleoccupant's presence and position, particularly of the occupant's head,which is closest to the roof-mounted sensor array, and for using thisinformation to enable, disable, or modify the deployment of an airbagsystem, the invention is useful in a number of other ways. One suchapplication is taught in parent application Ser. No. 08/535,576.Briefly, this invention utilizes sensor output to detect head noddingand other head motion which correlates to sleepiness of a driver, andthen to activate an alarm to alert the driver as well as operators ofother nearby vehicles to possible danger from the condition. As may bereadily understood, the sensor array may be dedicated to a singlefunction (e.g., airbag disabling/enabling or sleepiness detection), orto multiple functions (e.g., both airbag and sleepiness detectionfunctions).

Other useful applications that may be achieved concurrently include: Inthe case of head injuries caused by accidents, neurological diagnosiswould be enhanced by a record of head acceleration. The presentinvention is able to detect and record head acceleration at intervals of1 msec or faster, providing useful data to the neurologist. Data onpresence or absence of an occupant in each seating position permitsbroadcast of the total number of passengers in the motor vehicle. Thisis useful to report the number of passengers to authorities in the eventof an accident or to verify total passenger count of vehicles travelingin the "high occupancy lan" of divided highways, such as found in theWashington, D.C., metropolitan area. Passenger data can also be used tobalance and control the various heating, cooling, and sound systems inmotor vehicles.

While private passenger vehicles are most valuably served by the sensingtechnology of the present invention, similar applications may be foundin public transportation, such as to determine the number of occupiedversus empty seats on a bus, train, plane, or other rapid transitvehicle. This data can be further enhanced to provide revenueverification by recording the seat occupancy and storing appropriaterates or tariffs for the travel segment in a data processor. In anairplane, through-passenger count can be recorded automatically formulti-stop flights.

Regarding the comfort and convenience for an individual occupant,especially for the vehicle operator, the head position can be used toautomatically adjust side-mirrors which may be out of reach of theoccupant, as in a large truck. Also, if the head position is determinedin three axes, this data can be conveyed to a seat headrest adjustmentunit to insure that it is at the proper height to protect againstwhiplash in the event of an impact. While three-axis determination isoptimum for this application, a single or two-axis determination usingoutput from one or two sensors may be employed. The same capability maybe used to automatically adjust the entire seat position, raising theseat and moving it forward for a smaller occupant, or vice-versa for alarger occupant. The seat position would still be individuallycontrollable, however, allowing the occupant to fine-tune position forbest overall comfort for that individual.

Another valuable application of the sensing system is to electronicallylink driver presence to the ignition switch, to create an additionallayer of protection against vehicle theft. In this embodiment, a personentering and occupying the driver's seat without inserting a key in theignition within some appropriate time period would activate a theftalarm, and could disable engine electronics to prevent starting of thevehicle. This feature provides an added level of theft protection, inaddition to those presently available which detect bypassing of the doorkey or door lock codes.

For commercial truck operators, tracking driver presence over time,based on detecting head presence and position, can be a means ofassessing employee productivity, such as time driving versus notdriving, or can be used to detect excessive time behind the wheel,contrary to "hours of continuous service" regulations for long-haultruckers. In the military, there are conditions in which the equipmentoperator is required to use optical sighting devices for targetacquisition, while traveling at high speed over rough terrain. The headmotion of the equipment operator and the fixed position of the sightingdevice may come into conflict, resulting in various failure modes. Thepresent invention may be employed to automatically adjust the positionof the optical sighting device using the head x,y,z, coordinatesdetermined by the sensor array and processing circuitry.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverin the appended claims all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above, and of the corresponding application(s), arehereby incorporated by reference.

What is claimed is:
 1. A capacitive coupling sensor array comprising afirst sensor having a first geometry and a second sensor having a secondgeometry, said first and second sensors being placed such thatequipotential lines of said first and second sensors overlap.
 2. Thecapacitive coupling sensor array of claim 1 wherein said first andsecond geometries are selected from the group consisting of circular,oval, square, rectangular, triangular, and polygonal of greater thanfour sides.
 3. The capacitive coupling sensor array of claim 1 whereinsaid sensor array is mounted proximate a roof of a motor vehicle.
 4. Thecapacitive coupling sensor array of claim 3 wherein a long axis of saidfirst sensor is perpendicular to a long axis of said second sensor. 5.The capacitive coupling sensor array of claim 4 wherein said firstgeometry is rectangular and said second geometry is oval.
 6. Thecapacitive coupling sensor array of claim 5 wherein said first sensor isrearward of said second sensor in said motor vehicle.
 7. A vehicleoccupant sensing system comprising one or more capacitive couplingsensors, said sensors comprising a receive electrode and a driveelectrode, said receive electrode placed within said drive electrodesuch that a spacing between edges of said receive electrode from saiddrive electrode is non-homogenous, said sensors generating equipotentialfield lines of non-uniform curvature.
 8. The vehicle occupant sensingsystem of claim 7 wherein said sensors are mounted proximate a roof of amotor vehicle.
 9. A vehicle occupant sensing system comprising one ormore capacitive coupling sensors, said sensors comprising a flexiblecircuit board adhered and electrically contacted to a flexibleconnector.
 10. The vehicle occupant sensing system of claim 9 whereinsaid sensors are mounted on a curvilinear portion of a roof of a motorvehicle.
 11. A dynamically variable capacitive coupling sensorcomprising at least three electrodes in a concentric arrangement, eachof said electrodes being sequentially configurable as a drive electrode,grounded gap, and receive electrode.
 12. The dynamically variablecapacitive coupling sensor of claim 11 wherein said sensor is mountedproximate a roof of a motor vehicle and is comprised by an occupantsensing system of said motor vehicle.
 13. A motor vehicle occupantsensor comprising a plurality of capacitive coupling sensors, whereineach of said capacitive coupling sensors comprises a capacitive couplingdetector driven by a electrical driving means, wherein each of saiddetectors comprises two electrodes, wherein said driving means comprisesan oscillator connected to one of said electrodes, and wherein signalprocessing means are connected to the other of said electrodes.
 14. Themotor vehicle occupant sensor of claim 13 wherein a single oscillatordrives all of said capacitive coupling sensors.